How should I insulate hydronic radiant heating under floorboards

Question

A couple weeks ago a contractor installed hydronic radiant heating at my place. The building is two floors (studio above a garage) and the heating was installed under the floorboards. When he finished installing the piping and pumps he told me I'd need to install reflective insulation.

After a few google searches I'm seeing mixed information on whether reflective barriers/insulation works or not. Some sites claim more heat is lost to the lower floor than the upper floor where the heat is intended to go (not that that's entirely a bad thing, the garage isn't heated and it's my workout/laundry room). They suggest using regular foam insulation.

My questions are:

1. Do I need the reflective barrier/insulation?
2. If I need reflective barrier/insulation, do I also need foam insulation installed?

Brand suggestions are also appreciated.

Answer 1

theory is that the pipes are hot enough that radiation is signficant. Putting a low IR emmisivity surface reduces the amount of radiant energy the bottom of the cavity absorbs.

If you just have a low e foil, then you cut the radiation in half. However by conduction the entire air space gets warm. So you will have the foil as a barrier for conduction too. It's not very good at that.

Me, I would put friction fit paper backed bats in. leave a 2" thick air space at the top of the cavity, so that you have fewer hot/cold spots on the floor above.